Our major long-term objective is to understand the synaptic connections of the neurons that underlie visual processing in the vertebrate retina and, to ascertain how the visual image is integrated into parallel ganglion cell pathways for transmission to the brain. Our studies over the years have used the turtle retina in addition to mammalian retinas mainly because certain functional pathways have often been more easily elucidated in this cold-blooded, highly visually-dependent vertebrate: particularly pathways concerning color. It turns out that morphological and physiological examination of turtle retina together with pharmacological and behavioral studies have been proceeding so rapidly in the last decade, that the turtle retina is now one of the best studied in retinal research. We have been major contributors to these studies and we think that we can continue to integrate anatomical and electrophysiological findings with greater advantage in this retina than in others. The emphasis of this grant proposal is directed at seeking general principles of retinal organization concerning tangentially and radially organized mosaics and pathways involved in spectral processing. Specifically we will: 1) Investigate whether the different spectral types of photoreceptor are arranged into repeating units or an organized mosaic; 2) Determine the spectral inputs and ultrastructure of synaptic contacts to cone pedicles of intracellularly recorded and HRP -injected color-coded bipolar cells and see how they fit into the photoreceptor mosaic; 3) Look at spectral contacts of chromaticity H2, H3 and H4 cells with the objective of linking the color-coded bipolar and horizontal cells into pathways arising from the photoreceptor mosaic; 4) Ascertain whether Muller cells divide patches of retina into continuous "columns" of organized color units from photoreceptors through bipolar cells to a group of ganglion cells subserving this column, and 5) In collaboration with Richard Normann and Josef Ammermuller, who are recording turtle ganglion cell responses with multiple electrode arrays, attempt to understand the architecture of color- coded ganglion cell that are involved in their recordings.